In general, in a motor vehicle engine, or other machine which utilizes a chain, a belt, or the like as a power transmission medium, a fixed or movable guide over which the transmission medium slides, is attached, by a mounting bolt, a pin, or a similar fastener, to an engine block, or to another frame member.
A movable guide, such as a tensioner lever or the like used in such a transmission device, imparts appropriate tension to a power transmission medium in order to prevent transmission failure due to excess stretching, or excess loosening of the circulating power transmission medium. A fixed guide, such as a guide rail or the like, limits the power transmission medium to a predetermined path of travel in order to prevent the power transmission medium from producing vibration noise, and to prevent sideward vibration, and disengagement.
A conventional movable guide, such as the chain tensioner guide 100 depicted in FIG. 10, is typically molded from a single synthetic resin. The guide 100 comprises a slide rail 101, which is in sliding contact with a traveling, power-transmitting chain C, and a rail supporting member 102 extending longitudinally along the back side of the slide rail. Referring to FIGS. 10 and 11, the rail supporting member 102 includes a boss 102a, having a mounting hole 103, allowing the rail supporting member to be attached to an engine block or the like so that it can function as a movable guide. A tensioner (not shown) abuts a tensioner abutting portion 102b of the rail supporting member 102 in order to apply the appropriate tension to the chain, thereby preventing excessive stretching, or excessive loosening, of the chain, either of which could result in transmission failure. Ribs 102c serve to reinforce the guide while minimizing its weight.
In the conventional guide 100, which is integrally molded from a single synthetic resin, the maintenance of good sliding contact and wear resistance in the slide rail 101 is incompatible with the achievement of adequate strength in the supporting member 102, especially in the environment of a motor vehicle engine, where temperatures around 200° C. may be encountered. When the guide 100 for the transmission device is molded from a plastics material having superior sliding contact properties and wear resistance, other desirable mechanical properties of the guide 100, such as strength, are sacrificed. Furthermore, when the cross-section of the guide is increased to compensate for its inadequate strength, the larger size of the guide requires more space, and makes installation of the guide onto an engine block wall more difficult.
To solve the above-mentioned problems a slide, proposed in Japanese Patent No. 2818795, includes a supporting member consisting of a high strength synthetic resin and a slide liner consisting of a synthetic resin having good wear resistance connected to the supporting member. Either the supporting member or the sliding lining body was used as a mold, and the other was injection molded. As an alternative, a chain tensioner described in Japanese laid-open Patent Publication No. Hei. 8-254253, was insertion-molded using a steel sheet as a core. In Japanese laid-open Patent Publication No. Hei. 9-324839, a guide rail was proposed in which a slide path liner was fitted to a carrier by a friction locking system.
To produce the slide disclosed in Japanese Patent No. 2818795, where either the supporting member or the slide lining body was used as a mold, and the other was injection molded, two molding steps were required. Moreover, to integrate both synthetic resin elements, it was necessary to form a dovetail groove by molding. Consequently, the mold structure became complex and manufacturing cost was increased.
In the chain tensioner disclosed in Japanese laid-open Patent Publication No. Hei. 8-254253, deformation could be generated in the guide itself as a result of the difference between the coefficients of expansion of the steel core material and the plastics material, resulting in breakage. Moreover, because of the weight of the steel core material it was not possible to achieve a weight reduction.
In the guide rail disclosed Japanese laid-open Patent Publication No. Hei. 9-324839, where the slide path liner and the carrier were fitted together releasably by a friction locking system, the manufacturing steps were complex, the manufacturing cost was high, and the friction locking portion was subject to breakage.
Accordingly, in prior art tensioner guides, reliability and mechanical strength of the guide rails were not entirely satisfactory.